Note: Descriptions are shown in the official language in which they were submitted.
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4-167 CVE~339
IMPROVED MAGNETIC SENSING PROXIMITY DETECTOR
Background
The present invention relates to an improved magnetic
sensing proximity detector. Magnetic sensing proximity
detectors have been used previously to detect the close
5 pressnce of a ferrous metal mass. In one form these
detectors have includes a central hollow magnet with end
magnets supported on a rod connecting them which extends
through the opening in the central magnet. A switch is
connected at one end of the two connected magnets to be
10 operated by the movement of such two magnets relative to
the central magnet and the housing in which it is secured.
The approach of a ferrous metal close to the end of the
magnet away from the switch end causes the magnets and
their connecting rod to move toward the ~errous metal to
15 thus changs the position of the switch. An example of
this type of magnetic sensing proximity switch is dis-
closed in U. S. Patent No. 4,117,431.
Another type of magnetic sensing proximity detector
is shown in U. S. Patent No. 4,674,338 in which a central
20 magnet is positioned within two annular magnets so that
the movement of the central magnet which is normally
biased in one direction by the positioning of the poles of
the three magnets, moves in the opposite direction when a
magnetic material approaches sufficiently close to change
25 the forces on the central magnet to overcome the force
biasing it toward the one direction.
;~ A further type of magnetic sensing proximity detector
is shown in U. S. Patent Nos. 3,176,096 and 4,225,837
wherein side-by-side magnets are used so that the position
30 of the switch arm is normally in one position and pivots
to the opposite position on the approach of a ferrous
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metal within the range oE sensitivity of the detector.
The latter patent is stated to be an improvement on the
former patent.
One disadvantage which has been experienced with the
5 prior magnetic sensing proximity detectors is their very
limited range in which they can sense the approach a
ferrous metal material and the fact that such prior
devices are not adjustable to preselect the exact point at
which the approach of ferrous metal causes the detector to
10 change its position.
Summary
The improved magnetic proximity detector includes a
tubular housing, a kubular magnet fixed in position within
the housing, a first movable magnet within said housing at
15 one end of said tubular magnet, a second movable magnet
within the housing at the other end of the tubular magnet,
~ an annular magnet positioned in surrounding relationship
; to the housing, means for adjusting the position of the
. annular magnet to control the sensitivity o~ the assembly,
20 means connecting the first magnet and the second magnet, a
switch including a blade, a first contact and a second
contact, means connecting said first and second magnet to
said blade so that movement of said first and second
magnets moves said blade between contact with the first
25 and second contacts, the first magnet having its poles
, ; arranged so that it is attracted to said tubular magnet,
said second magnet having its poles arranged so that it is
repelled by said tu~ular magnet, the nea~ness of a
ferrous metal to the end of said housing containing said
30 first magnet moving the two magnets and the blade to
- change the position of the switch, adjusting the axial
position of said annular magnet changing the flux from the
: end of the housing containing the first magnet to adjust
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the dlstance at whlch a ferrous metal causes the change of
positlon of the swltch blade.
An ob~ect of the present lnvention ls to provide an lmproved
magnetlc proxlmlty detector whlch has lncreased range of
sensltlvity to ferrous metal.
A Eurther ob~ect is to provide an improved magnetlc pro~lmlty
detector which has an ad~ustable range of sensitlvlty to ferrous
metals.
Thus, according to a broad aspect of the lnventlon, there ls
dlsclosed a magnetlc proxlmlty detector for ferrous metals
comprlslng a houslng, an assembly of magnets, at least one of
whlch ls movable, posltloned wlthin sald houslng, a swltch, means
connectlng the movable magnet to the swltch to change lts posltlon
when the magnet moves, sald movable magnet being blased to one
position by the other magnets of sald assembly and movlng to lts
other positlon responslve to the presence of a ferrous metal
wlthin lts effectlve sensitlvlty range, and means for focuslng the
flux of sald magnets to change the effectlve sensltlvlty range for
movement of sald movable magnet responslve to the presence of a
ferrous metal.
Brief Descrlption of the Drawin~s
These and other ob~ects and advanta~es of the present
lnventlon are herelnafter set forth wlth respect to the drawlngs
wherein:
FIGUR~ 1 is a longltudlnal sectlonal vlew of the lmproved
magnetlc proxlmlty detector lllustratlng the components ln one
position which does not indicate the presence of ferrous metal.
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FIGURE 2 ls a slmilar sectlonal vlew of the detector but
showing the components ln thelr opposite position as a result of
the detectlons of a ferrous metal.
FIGURE 3 ls a schematlc view of the three magnets used with
proxlmlty detectors of the prior art and illustrates the relative
position of the poles of the magnets and thelr flux fields.
FIGURE 4 ls a schematic vlew of the three magn~ts used ln the
detector o~ the present invention and lllustrates the relative
position of the poles of the magnets, their flux fields and the
focusing effect on the flux field at the end of the detector
resulting from the annular focusing magnet.
Description of the Preferred ~mbodiments
The lmproved structure of the present lnvention is shown in
FIGURES 1 and 2. Detector 10 includes houslng 12, tubular magnet
14 secured wlthin houslng 12, assembly 16 of movable magnets, and
switch contacts 24 and 26 and
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blade 28. Movable magnet 18 is positioned in end 29 of
housing 12 and has its poles arranged with respect to the
poles of tubular magnet 14, as shown, so that it is
attracted by tubular magnet 14. Movable magnet 20 is
5 positioned within housing 12 on the opposite side of
tubular magnet 14 ~rom magnet 18 and has its poles
arranged with respect to the poles of tubular magnet 14,
as shown, so that it is repelled by tubular magnet 14. A
suitable non-magnetic closure 29a is positioned across end
10 29 of housing 12.
Connecting means 22 includes rod 30 extending through
the central axial opening of tubular magnet 14 with
support by low friction plastic bearings 32 and 34 which
are positioned in the ends of the axial opening through
15 tubular magnet 14 as shown. One end of rod 30 is con-
nected ts movable magnet 18 and the other end is connected
to movable magnet 20. Extension 36 connects to movable
magnet 20 and is secured to blade 28 which is pivotally
mounted to contact 37 so that movement of magnet assembly
20 16 moves blade 28 between positions engaging contacts 24
and 26. In the position shown in FIGURE 1 blade 28
connects contact 37 with contact 26.
Annular magnet 38 is positioned around the exterior
of housing 12 generally at a position surrounding movable
25 magnet 18. Nuts 40 and 42 are threaded onto threads 44 on
the exterior of housing 12 on either side of annular
magnet 38 to secure it in a preselected pssition with
respect to movable magnet 18. Nuts 40 and 42, or other
suitable adjustable positioning means, are used to adjust
30 the position of annular magnet 38 which adjusts the range
~: of sensitivity of the structure as hereinafter explained.
As shown in FIGURE 1 movable magnet assembly is in
its right position with blade 28 in engagement with
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contact 26 since ferrous mass 46 is spaced outside the
sensitivity range of detector 10.
Mass 48, shown in FIGURE 2, is positioned closer to
detector 10 so that is within the sensitivity range,
5 considering the position of annular magnet 38 and assembly
16 has been moved to its left causing blade 28 to move
into engagement with contact 24 to complete the circuit
between contact 37 and contact 24. It should be noted
that annular magnet 38 is shown including pole pieces 38a
10 and 38b but may be used without such pole pieces.
Dashed line 49 in FIGURE 3 illustrates the outer
limit of the sensitivity range for detector 10 when
annular magnet is not used with detector 10. Detector 50
shown in FIGURE 3 is illustrative of the prior art
15 detectors. Detector 50 includes movable magnet 52, fixed
tubular magnet 54 and movable magnet 56 controlling the
position of blade 58. Detector 50 does not include an
external annular magnet for focusing the flux field as
hereinafter describ~d. With detector 50 as shown in
20 FIGU~E 3, the sensitivity range is limited ~o a maximum of
0.10 inch.
FIGURE 4 is a schematic illustration of proximity
detector 110 which is the same structure as detector 10
previously described and the components shown are given
25 the same number for identification with the prefix numeral
"1". A comparison of the flux field of movable magnet 118
with the flux field of movable magnet 52 illustrates the
focusing effect of annular magnet 138 on the flux field to
flatten the field and cause it to extend a greater
30 distance beyond the end of magnet 118 than it would extend
without annular magnet 138. Dashed line 149 is drawn in
position with respect to the end of the housing to
illustrate the outer limit of the sensitivity range of
detector 110. In comparison the the maximum range of
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sensitivity of detector 50 being 0.10 inch, the maximum
range of sensitivity for detector 110 having all of the
same components as detector 50 except for the addition of
annular focusing magnet 13~ is approximately 0.50 inch.
5 Additionally, the adjusting of the position of annular
focusing magnet 138 provides an adjustment of the focusing
of the flux field of movable magnet 118 to preselect the
exact distance at which a ferrous metal will cause a
change in the position of blade 128.
It should be noted the present invention has applica-
tion to other types of magnetic proximity sensing devices,
particularly to a device which includes at least three
magnets with at least one magnet movable with respect two
fixed magnets in a housing as discloses in U. S. Patent
15 No. 4,674,338.
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